Field of Invention
The present invention relates generally to hinge constructions, and more particularly to a security hinge construction including a concealed radiative emitter and detector for detecting hinge leaf movement. The hinge construction may be included in an external alarm or monitor system which monitors the relative position of the hinge, i.e., whether the hinge is opened or closed.
General Background
Monitoring the state of a door is desirable in a variety of situations such as fire control, environmental control, and prisons or other security systems, to name a few. Specifically, in the case of security systems, there are two primary objectives in monitoring any portal of ingress or egress. First, the monitoring system must be reliable and tamper-proof. Second, the monitoring system should be concealed from observation of would be intruders or confined persons to prevent sabotage. In the past, door monitoring has generally been accomplished through the sensing of a change in position of some part of the door assembly, e.g., the door relative to the door jamb; or, the rotation of the door relative to some fixed point.
To accomplish these objectives, prior monitoring systems have utilized a variety of different sensing means to detect the state of the door. Such prior sensing systems have included electro-mechanical means, such as a simple contact switch mounted on the hinge leaves as disclosed in U.S. Pat. No. 499,428 or a series of rotating contacts concealed in the hinge as disclosed in U.S. Pat. No. 3,838,234. Other systems have included electro-magnetic switches such as disclosed in U.S. Pat. No. 4,062,314 and more complicated electro-mechanical switches, as disclosed in U.S. Pat. No. 4,016,381. To protect against tampering or sabotage, electro-mechanical switches have been concealed in the hinge body. This method of concealment was disclosed in several U.S. patents, including U.S. Pat. No. 4,049,934; U.S. Pat. No. 4,168,409; and U.S. Pat. No. 30,716.
Non-mechanical means of sensing having also been used in a number of different security systems. A magnetic flux detection system was disclosed in U.S. Pat. No. 3,772,669, which operated in combination with a mechanical means for moving a magnetic pole piece. Radiative emitter and detector systems were disclosed in U.S. Pat. No. 4,394,584; U.S. Pat. No. 4,583,082; U.S. Pat. No. 4,507,654; and U.S. Pat. No. 4,629,883.
Each of these prior non-mechanical monitoring systems fail to meet one of the objectives in a security situation as they are not concealed. These systems invited tampering which resulted in false indications from the sensing means or system failure. Electro-mechanical sensing systems have a number of disadvantages in that they are subject to wear and, in many cases, sabotage, tampering or false readings.
In contrast to these prior systems, the present invention eliminates the disadvantages inherent in electro-mechanical systems through the use of a concealed non-mechanical sensing means. The present invention also provides an inexpensive, simple system which is easy to install and requires a minimum of special construction or adaptation.